1. Field of the Invention
The present invention relates to a coupler for attaching a farm implement to a tractor.
2. Prior Art
Farm tractors are regularly used to pull various soil working or treating implements. Most tractors are fitted with a three point hookup used to attach the implement to the rear of the tractor. The three point hookup includes two vertically adjustable lower trailing arms and an upper trailing arm extending rearwardly from the tractor. The upper trailing arm is usually attached to the implement at a point above the attachment of the implement to the lower trailing arms.
The lower trailing arms are adjustable to set the height of the front end of the farm implement relative to the ground. In some configurations, the upper trailing arm is adjustable to vary the attitude of the implement relative to the ground and to the tractor. However, in other applications, the upper trailing arm serves as a stabilizer for the farm implement. For example, in bedding plows which rotate about an axis parallel to the line of travel for engaging alternative sets of plows into the soil, the upper trailing arm acts as a stabilizer for torsional loading induced by rotating the plow between its alternative positions.
Although the attachment of an implement to a tractor through both the lower and upper trailing arms provides a stable connection, this arrangement creates problems when the tractor and implement are operated over irregular terrain. Because the attachement of the implement to the tractor is fixed at three points, when the tractor and implement traverse a valley, the fixed attachment causes the implement, such as a plow, to be forced downwardly into the soil. Alternatively, as the tractor and implement traverse a crest or hill, the attachment tends to withdraw the implement out of the soil. Thus, where an implement is adjusted to the proper setting for operation over a level terrain, this setting is disturbed when the tractor and implement traverse a valley or crest in the field in which the machinery is operated.
Therefore, a need has arisen for an apparatus for attachment between a tractor and farm implement for compensating for irregularities in the terrain while permitting the three point attachment normally required between the tractor and implement.